FRIDAY, March 3, 2017 (HealthDay News) -- The number of U.S. teens who use indoor tanning has dropped by half in recent years, a new government study reveals.

Only about 7 percent of high school students said they used indoor tanning in 2015, down from almost 16 percent of students in 2009, according to results from a U.S. Centers for Disease Control and Prevention survey.

But that still leaves more than 1 million teens putting themselves at increased risk of skin cancer, including the most severe form, melanoma, by going to a tanning salon, said study lead author Gery Guy Jr.

Worse, their use of indoor tanning appears to give them a false sense of security when they step outdoors into real sunlight, said Guy, a health economist with the CDC's division of cancer prevention and control.

"We also found that among the 1.2 million high school students who are continuing to indoor tan, 82 percent of them experienced a sunburn in the past year," Guy said. That increases the danger, he added.

Just one blistering sunburn during childhood or adolescence can nearly double your lifetime risk of melanoma, according to the American Academy of Dermatology.

Teens likely believe the myth that indoor tanning provides a "base tan" that will protect them against sunburn, Guy said.

"There is no base tan. Tanned skin is damaged skin," Guy said. "Individuals may think a base tan will protect them, when in reality it doesn't."

The CDC's Youth Risk Behavior Survey of thousands of high school students focuses on risky behaviors that could pose a hazard to kids' health and safety.

As part of the survey, teens were asked how often they'd used an indoor tanning device (such as sunlamp, sunbed or tanning booth) during the previous 12 months. They were also asked how many times they'd been sunburned.

Indoor tanning is most popular among white girls. But even that group experienced a large decrease in trips to the tanning salon -- dropping from more than 37 percent in 2009 to just over 15 percent in 2015, the findings showed.

Unfortunately, white girls' interest in indoor tanning appears to increase with age, and the study found that about one out of every four girls 17 or older was still using tanning beds.

Dr. Len Lichtenfeld is deputy chief medical officer of the American Cancer Society. He said, "The reality that one-quarter of women 17 and older are using indoor tanning is still very disturbing. It basically says there's a huge market for indoor tanning, and young people are still taking advantage of that opportunity."

A wave of state laws restricting teens' use of tanning beds likely has been the major driver in the observed decline, said Guy and Dr. Henry Lim, a dermatologist with Henry Ford Hospital in Detroit.

Only five states had laws restricting indoor tanning in 2009, but by 2015 such laws had been enacted in 42 states, according to the report.

"Most of them are not bans, but restrictions that you have to get parental consent to go to a tanning booth," said Lim, who co-authored an editorial accompanying the study. "I think it is a sort of deterrent."

The U.S. Food and Drug Administration had proposed a federal rule restricting access to tanning beds for kids under 18, but it remains just that -- a proposal, Lichtenfeld said.

The World Health Organization has classified indoor tanning devices as cancer-causing. And, Guy said, in 2014 the U.S. Surgeon General's Office listed limiting indoor tanning as one of its strategic goals for skin cancer prevention.

Unfortunately, U.S. schools do not seem to promote sun safety, according to a second CDC study. Both were published online March 3 in the journal JAMA Dermatology.

Researchers found that sun-safety practices are not common among schools, particularly in high schools.

For example, only about 37 percent of high schools required teachers to give students time to apply sunscreen, compared to about half of elementary and middle schools.

Even then, kids who didn't bring their own sunscreen were mostly out of luck. Just over 13 percent of schools said they provide sunscreen for kids' use.

Lim believes that restrictions on indoor tanning and continued public education will continue to decrease the number of teens hitting the tanning salon.

"I think we're on the right track, and we need to keep going," Lim said. "It's similar to smoking. It takes a concerted effort to get people to change their behavior."